1. Field of the Invention
The present invention relates to a fluid measurement sensor attachment structure. More specifically, the present invention relates to a fluid measurement sensor attachment structure with which measurements can be performed at high precision without lowering a fluid transport capacity.
2. Description of the Related Art
Various fluid measurement sensor attachment structures have been provided in order to measure properties such as the flow rate, the fluid pressure, and the transparency of a fluid passing through a pipe. Examples thereof include an attachment structure in which a sensor is disposed in one of three branch pipes of a T-joint, and the flow rate and the like of a fluid flowing through the remaining two pipes are measured. Japanese Laid-Open Patent Publication No. 9-166512 describes that a fluid pressure sensor provided with a cylindrical sensor casing that is fitted to an inner wall of a joint base end portion and that has a diaphragm on the bottom portion is proposed as a sensor for the measurement. Furthermore, Japanese Laid-Open Patent Publication No. 11-64048 describes that, as a technique for improving the sealing performance between a sensor casing and a joint main body, a fluid measurement sensor attachment structure is proposed that includes a joint main body, a cylindrical sealing member, a sensor casing accommodating a fluid measurement sensor, and a pressure ring, wherein a joint is sealed with the cylindrical sealing member by causing the pressure ring to press the cylindrical sealing member against the joint main body.
The sensor of Japanese Laid-Open Patent Publication No. 9-166512 and the attachment structure of Japanese Laid-Open Patent Publication No. 11-64048 are both premised on the assumption that the sensor is attached to an existing T-joint as shown in FIG. 7. This attachment structure uses a structure for connecting a T-joint and another pipe. Accordingly, a sensor 3 is positioned near a connecting portion C, and the sensor 3 is away from a flow path P, and, thus, the flow rate, the fluid pressure, and the like may not be accurately measured. Furthermore, since a turbulent flow occurs at the branching portion, a fluid accumulation or a pressure loss may occur, which may lower the fluid transport capacity.
It seems that the measured values become closer to accurate ones by projecting the sensor 3 to a point near the flow path P. However, the problem that the transport capacity is lowered cannot be solved by merely arranging the sensor close to the flow path because a turbulent flow occurs due to a fluid flowing into a point between the sensor 3 and a branch pipe 2a. 